The raw mill not only grinds the material it also dries it. The required air flow depends upon the raw material massflow and the moisture. Air flow control of the raw mill is very important since the ID fan consumes almost 60% of the energy of the mill. With PROMECON technology air flow measurement can be installed after the cyclones or with a special erosion protected version of the sensors even before the cyclones. Holcim at the Midlothian plant calculated savings of 0.5-1 kWh/t raw meal by utilizing MECONTROL automated draft control.
Raw Mill Bypass Ducts
Depending on raw material moisture some plants do not need all of the kiln exhaust gas to dry the raw meal during grinding, so they may have multiple ducts that bypass the raw mill and then enter the raw mill discharge. The drift free McON air system can be used for material balance.
Cyclones are simple but effective separators. The performance of cyclones depend on the flowrate of the charge and the discharge pipes. Using PROMECON technology the flow rates can be precisely measured.
Precalciner - Calciner
Pulverised coal together with ground raw material flows through the calciner. Control of the calcination process requires measurement of the air as a carrier for those solids.
Preheater downcomer duct – kiln ID-fan inlet
The kiln ID-fan is usually controlled by the amount of excess air in the combustion process (%O2). Measuring the actual exhaust gas flow from the kiln opens up new possibilities for controlling the overall draft through the system. The MECONTROL Air System offers an accurate, drift free flow metering solution without additional pressure drop in the down comer duct.
For direct fired kilns it is critical to maintain a controlled primary air flow to maintain the correct flame shape. Flames which are "too bushy" can overheat the refractory and cause a premature and costly outage for repairs.
Secondary air as the major combustion air for the kiln pre-heated by the clinker cooler further reduces the energy demand of the plant. Correct balancing can be done with PROMECOM technology.
Tertiary Air (TA)
Up to 60% of the plants fuel can be burnt in precalciners using tertiary air from the clinker cooler. For optimum plant throughput and efficiency the amount of air through the TA duct needs to be balanced with the air through the kiln. PROMECON delivers flow measurement solutions for TA ducts covering a temperature range up to 1000°C/ 1850°F
Finished Product Mill
For either mill type airflows need to be controlled for efficient operation. Existing units are usually ball mills. Air flowmeters are used to control the mill sweeps and separator for maximising efficiency. New plants or retrofits have been utilizing vertical roller mills to reduce electrical consumption. The total air flow through the VR-mill must be controlled for efficient operation
Air from Grate Cooler
is hot and contains clinker dust. Applying PROMECON technology to the different ducts of the cooler let’s the operator know exactly the flow balance and where the air is going.